Prediction Of Liquid Accumulation In Gas Pipeline

Liquid accumulation is a common phenomenon in natural gas production systems,which will have adverse impacts on the normal operation of the system.Accurate prediction of liquid accumulation in pipeline will help designers and operators take measures in time to mitigate the detrimental impacts,and determination of critical gas velocity is the key to the prediction of liquid accumulation in gas pipeline.The related studies on the prediction of liquid accumulation in pipelines are reviewed,and the limitations of the minimum pressure drop model and the liquid droplet model are pointed out.Based on the existing experimental observation,the liquid film model is considered applicable.The multiphase flow models are developed and the liquid accumulation in wellbore and wet gas pipeline are predicted in this paper.Annular mist flow is the dominant flow pattern in the wellbore.In consideration of the droplet entrainment in gas core and the uneven film distribution along the circumference of the tubing in deviated gas wells,a practical model is proposed to judge the liquid loading of gas wells with different tubing diameters and angles of inclination.Based on the indoor experimental data of Guner and Alsaadi and the field operating data given by Turner and Veeken,the new model is compared with Barnea model,Luo model,Turner model,Belfroid model,Mul Flow flow regime transition model and Mul Flow minimum shear stress model,and each model is quantitatively evaluated.From the accuracy of the prediction results,the new annular mist flow model is better than the other models,and can be used to determine the liquid loading of gas wells accurately and conveniently.For wet gas gathering pipeline,the stratified flow is the dominant flow pattern.This paper adopts “the minimum-slip criteria” as the flow regime transition criterion and a theoretical model of gas-liquid two-phase flow is developed,which can calculate the critical gas velocity directly under different conditions.On the other hand,it is found that a multi-solution area occurs to the combined momentum equation of stratified flow at low liquid loading,and that the superficial gas velocity corresponding to the left boundary of the liquid holdup multi-solution zone is almost the same as the one calculated by the flow regime transition criterion based on the "minimum slip" criterion.The experimental data of Fan and OLGA software are used to verify the model,and the values of critical gas velocity calculated by the model are relatively reasonable.The results show that the inclination angles,pipe diameters,operating pressures and liquid flow rates have effects on the critical gas velocity.Under the condition listed herein,the critical gas velocities increase with the inclination angles,pipe diameters and liquid flow rates,and decrease with the operating pressures.